When 7-oxodesacetamidothiocolchicine ( 1) was treated with various peroxides in order to afford a Baeyer-Villiger rearrangement, a complex mixture of products was formed, which included the sulfoxide, ( 2) and sulfone, ( 3). When peracetic acid was used two additional products were formed; a C-ring lactone ( 4) and a ring-contracted allocolchicine derivative ( 5). The sulfoxide ( 2) was semi-preparatively resolved into enantiomers by chromatography on microcrystalline triacetylcellulose. Rotational barriers around the A - C pivot bond of 2, 4 and 5 were determined by dynamic H-1 NMR analysis. The compounds 2, 3, 4 and 7a exhibit moderate inhibition of tubulin polymerization, according to in vitro turbidity studies, whereas 5 was inactive.